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Iceland and Hawaii are both located on large scale division lines of lower mantle. That explains the volcanic activity within both areas. This can be found because convection rolls of equal hight and width fit into the layer, and the horizontal curvature of the rolls can be calculated.

The red curved lines show up-welling division between large scale convection rolls, spanning 30° from east to west. The blue curved lines show down-welling division between large scale convection rolls. Iceland and Hawaii are both found on such up-welling lines. This is the most basic feature of the convection rolls system.

The large convection rolls, spanning 30° from east to west, rule the main trend of tectonic drift. But the smaller rolls above, spanning 1.5° from east to west, make it more complicated. The Great Rift Valley of Africa is located above a main division line of up-welling within the lower mantle. At equator, the difference between convergent and divergent small scale rolls can be examined.

The red lines show the different points, one local diverging point, one large scale diverging point which is at the same time a local converging point. This seems controversial, but is an inherent factor of the convection rolls system.

Scandinavia is marked by one convection roll of lower mantle. The coast of Norway is the down-welling side, and the up-welling is found east of the White Sea and Finland.

As Iceland is one of the Scandinavian countries, the system of a pair of rolls, with down-welling in the middle, more and less marks the area.

For those really interested, the middle of the Scandinavian Peninsula, and all Iceland, are found within an intersection zone of two different convection rolls, although closely related to each other. The rolls reaching from equator meet the rolls extending to the North Pole.

But for the sake of simplicity, this is the picture we should comprehend at first. Also, please note that this is found within a 3D globe, but this is an over-simplified 2D drawing 🙂

The distance between W-Greenland and W-Norway along the 64th parallel shows the location of large convection rolls below 410km depth.

This is the same result as along equator, where the distance of 60° is found between Africa and S-America.

The pair of convection rolls under the continental shelf of Norway along 66°N is shown here:

You can go further and visualize the next convection roll to the east, under the Norwegian mountains, as they span more or less the width of one convection roll.